Data communications system and method of data transmission

ABSTRACT

A 1553 data communication system having a primary data bus, a redundant data bus and a non-1553 data communication overlay system is provided. The non-1553 data communication overlay system comprises a non-1553 bus controller terminal and a non-1553 remote terminal. Each non-1553 terminal includes a non-1553 transmitter block connected to the primary bus and the redundant bus for sending non-1553 signals, a non-1553 receiver block for receiving non-1553 signals and a non-1553 receive path selection block. The non-1553 receive path selection block selectively establishes a receive path between the primary data bus or the redundant data bus and the non-1553 receiver block according to predefined receive path selection criteria. A 1553 data communication method is also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No.11/332,395, entitled “Approximate Linear FM Synchronization Symbols fora Bandwidth Configurable OFDM Modem”, filed on Jan. 18, 2006, which isincorporated here by reference.

FIELD OF INVENTION

The present invention relates to data transmission over MIL-STD-1553communications systems and more particularly to an overlay communicationsystem over existing MIL-STD-1553 communication systems and associatedmethod.

BACKGROUND OF THE INVENTION

The AS15531 databus, also known as MIL-STD-1553 or simply 1553, is anapproximately 30 year old technology that defines the electrical andsignaling characteristics for 1 Mbps communications over an asynchronousserial, command/response digital data bus on which messages are timedivision multiplexed among users. The transmission medium is a twistedwire cable pair. 1553 specifies all of the electrical characteristics ofthe receivers, transmitters, and cable used to implement the bus, aswell as the complete message transmission protocol. 1553 is designed forhigh integrity message exchanges between unattended equipment. Themessages are generally highly repetitive, and their content andperiodicity are all pre-planned.

The United States Department of Defense (“DoD”) requires the use of 1553as the standard for all inter and intra-subsystem communications on allmilitary airplanes, helicopters, ships and land vehicles. Originallyused only in mission avionics, 1553 is now used in flight criticalavionics, flight control, weapons, electrical power control, andpropulsion control. 1553 was originally published in 1973 for use on theF-16 military aircraft program. The current version of 1553 isMIL-STD-1553B (“1553b”), Notice 2, implemented in 1986.

1553 is generally utilized for hard real time communications, where amessage is expected to be communicated over the bus in a deterministicway with known latency and very low probability that the message is notdecoded successfully. For these critical communications, the standardspecifies a primary data bus as well as a redundant (default) bus,providing communications path redundancy (“dual bus redundancy”). Fordual redundant bus applications, 1553 requires that a terminal becapable of listening to and decoding commands on both buses at the sametime. A 1553 terminal transmits 1553 signals on only one bus at a time.Redundancy can be extended to more than 2 buses.

MIL-STD-1553B utilizes a primitive Manchester II bi-phase signalingscheme over shielded twisted pair cabling. This modulation scheme isbandwidth inefficient, with most of its signal energy concentratedaround 1 MHz. MIL-STD-1553b has little remaining capacity for existingapplications and leaves little opportunity to enable additionalcommunication capabilities.

The retrofitting of an aircraft to add new equipment, Line ReplaceableUnits (LRU's) and/or munitions, including new wiring, is a complexprocess, which can require many months of modification time and involvesubstantial expenses. When new digital devices are added to an aftermarket military or commercial aircraft, the addition thereof typicallyrequires new bus wiring or an expanded load on the already heavilyloaded aircraft wiring cockpit applications. New devices, that may onlyrequire minutes to install, often require an entire airframe to benearly disassembled to allow new wiring runs to the new devices.Furthermore, the new wiring adds weight to the aircraft and takes upspace, which is always disadvantageous in any airframe design,especially for high performance airframes in which maneuverability isimportant.

Furthermore, new equipment, such as LRUs or munitions, which areretrofitted to an airframe often require high bandwidth data linksbetween the new equipment to points in the airframe where control ormonitoring is performed. High bandwidth communications between state ofthe art digital equipments are necessary.

The Society of Automotive Engineers (SAE) Avionics Systems Subcommittee(AS-1A), in cooperation with SBS Technologies Inc., have investigatedthe use of Discrete Multi-Tone (DMT) signaling as a possible technologyto increase the data transfer capacity of existing AS15531 networks.Their findings are summarized in a white paper entitled “The Use ofDiscrete Multi-Tone (DMT) Signaling for Data Transmissions on ExistingAS15531 Networks”, published on 15 Aug. 1998, which is incorporatedherein by reference. Experimental studies have considered only apoint-to-point connection of commercial Digital Subscriber Line (DSL)modems over a 100 ft piece of MIL-C-17 AS155531 cabling. This workindicated that the cable becomes surface impedance unstable and lossy atfrequencies above approximately 10 MHz (see p. 5, paragraph 4.3). Inaddition, test results of standard AS15531 couplers used in this workindicated that the couplers had a band-pass capacity of between 2 and 3MHz. (see p. 5, paragraph 4.4). Simultaneous DSL and AS15531 traffic wasobserved in the case of a Multi-rate Symmetrical DSL (MSDSL) modem,however MSDSL telecom modems would begin reporting significant number oferrors if the AS15531 transactions were scheduled at frequencies aboveapproximately 10 MHz. In the case of an Asymmetrical DSL (DSL) telecommodem tested, AS15531 bus traffic was detected by the modems and wassignificant enough to reset the modem link. The study fails to indicatethe feasibility of an operable system that would allow existent 1553networks to operate in their multi-drop, dual-redundant architecture, ata data transfer rate above 1 Mbps and signaling frequencies aboveapproximately 10 MHz.

There is a need for an improved 1553 communication system with a datatransfer capacity above 1 Mbps that can be overlaid over an existent1553 network without rewiring.

SUMMARY OF THE INVENTION

An object of the invention is to provide an improved 1553 datacommunication system and method of data transmission.

Accordingly, the invention provides a 1553 communication system having aprimary bus and a redundant bus, comprising a non-1553 datacommunications overlay system. The non-1553 data communication overlaysystem has a non-1553 bus controller terminal and a non-1553 remoteterminal. Each non-1553 terminal includes a non-1553 transmitter block,a non-1553 receiver block and a non-1553 receive path selection block.The non-1553 transmitter block is connected to the primary bus and theredundant bus and sends non-1553 signals on these buses. The non-1553receiver block receives non-1553 signals from one of the buses on areceive path selected by the non-1553 receive path selection block. Thenon-1553 receive path is selectively established between the primarydata bus or the redundant data bus and the non-1553 receiver blockaccording to predefined receive path selection criteria. According tofurther embodiments, the receive path selection criteria may includemonitoring performance metrics for bus conditions such as Bit Error Rate(BER), Signal to Noise Ratio (SNR), channel capacity. Such metrics couldbe monitored periodically, as well as averaged over appropriate timeintervals, according to specific system topologies and communicationrequirements.

Furthermore, a communication method over a 1553 communication networksis provided. The method comprises the steps of transmitting 1553 signalson a primary bus or on a redundant bus according to a 1553 bus faultdesign and receiving 1553 signals from the primary and redundant buses.The method further comprises the step of transmitting non-1553 signalsover the primary bus and over the redundant bus and the step ofselecting a non-1553 receive path between either the primary bus or theredundant bus an a non-1553 receiver. The method also comprises the stepof receiving non-1553 signals on the selected receive path. The receivepath selection is based on predefined receive path selection criteria.

Advantageously, the invention provides retrofitting an existent 1553communication system for increased data transfer capacity, withoutrewiring and with minimal impact to the existent 1553 communications.

BRIEF DESCRIPTION OF DRAWINGS

The following detailed description, given by way of example and notintended to limit the present invention solely thereto, will best beappreciated in conjunction with the accompanying drawings, wherein likereference numerals denote like elements and parts, where:

FIG. 1 is a block diagram of a 1553 communication system according to anembodiment of the invention;

FIG. 2 is a block diagram of a non-1553 terminal for a 1553communication system according to an embodiment of the invention;

FIG. 3 is a flow chart of a method of selecting a receive path fornon-1553 signals within a 1553 communication system in accordance withan embodiment of the invention;

FIG. 4 is a block diagram of a 1553 communication system, according to apreferred embodiment of the invention;

FIG. 5 is a block diagram of a 1553b terminal, used within the systemshown in FIG. 4;

FIG. 6 is a block diagram of an OFDM terminal used within the systemshown in FIG. 4;

FIG. 7 illustrates a theoretical Power Spectral Density (PSD) plot of anOFDM signal and a 1553b signal within a 1553b communication system inaccordance with an embodiment of the invention;

FIG. 8 is a Power Spectral Density (PSD) plot of an OFDM signal and a1553b signal within a particular 1553b communication system inaccordance with an embodiment of the invention;

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the invention.However, it will be understood by those skilled in the art that thepresent invention may be practiced without these specific details. Inother instances, well-known methods, procedures, components and circuitshave not been described in detail so as not to obscure the presentinvention.

Reference is made now to FIG. 1, illustrating a 1553 communicationsystem 10 according to the invention. System 10 comprises a primary databus 20 and a redundant data bus 30, a Bus Controller (BC) terminal 100and a plurality of Remote Terminals (RT) 110, 111, 112. 1553 compatibledevices are in most cases analog, so in general, each of the RemoteTerminals includes a transceiver which converts the binary bit streamson buses 20, 30 to analog signals. The Remote Terminals also compriseencoder/decoder equipment and protocol controllers, as well as othernecessary components to interface to any higher layer sub-systems. TheBus Controller 100 is a terminal consisting of a superset of thecapabilities of the Remote Terminals 110, 111, 112, acting as the mediaaccess controller (MAC) to the buses 20, 30, utilizing acommand/response protocol. In embodiments of the invention operable inaccordance with the 1553 standard, only the Bus Controller 100 can issuea command on the buses while Remote Terminals only respond to a commandreceived from the Bus Controller 100.

Within the 1553 communication systems 10, Remote Terminal 110, 112 arecapable of sending and receiving 1553 signals over the primary andredundant buses 20, 30, whereas Remote Terminal 111 is capable ofsending and receiving non-1553 signals. Furthermore, BC 100 is capableof sending both 1553 and non-1553 signals. 1553 signals are definedherein as signals in accordance with 1553 standard signaling schemes,including but not limited to primitive Manchester II bi-phase signaling.Non-1553 signals are any signals that can be differentiated from 1553signals either in frequency domain, time domain, Laplace domain, or byany other method obvious in the art. Non-1553 signals must be generatedso as to enable co-propagation with 1553 signals through an existing1553 system along the primary and secondary buses 20, 30. Preferably,when co-propagating non-1553 signals, impact to the transmission of the1553 signals is minimal. Without limitation, Digital Subscriber Line(DSL) code gain methods such as Carrier-less Amplitude/Phase (CAP)coding and Orthogonal Frequency Division Multiplexing (OFDM), closelyrelated to Discrete Multi-Tone (DMT) coding are particular examples ofpossible non-1553 signals.

Terminals capable of either sending or receiving non-1553 signals, suchas 111, are defined herein as non-1553 terminals or non-1553communication devices. Likewise, terminals capable of receiving 1553signals, such as 110 and 112, are defined herein as 1553 terminals or1553 communication devices. It will be recognized by those skilled inthe art that 1553 terminals and non-1553 terminals as defined herein aredifferentiated by their functionality and signaling capabilities, buttheir implementation may take various forms. Physically, they might beintegrated on the same IC or be built on different boards, but also theymight occur at different physical locations, all according torequirements of the communication system and to manufacturingpreferences. In an alternate embodiment, two distinct BC terminals, onecontrolling 1553 RT's and the other controlling the non-1553 RT's, mightbe provided.

Referring now to FIG. 2, a non-1553 terminal 111 according to anembodiment of the invention is illustrated. The non-1553 terminal 111comprises a non-1553 transmitter block 40 connected to the primary bus20 and the redundant bus 30 of a 1553 communication system, for sendingnon-1553 signals on these buses. The non-1553 terminal 111 alsocomprises a non-1553 receiver block 50 for receiving non-1553 signalsvia a receive path to be established with one of the primary bus 20 andthe redundant bus 30, by a non-1553 Receive Path Selection block 60. Asit will be recognized by someone skilled in the art, the non-1553Receive Path Selection block 60 comprises means for selecting one of thedata buses based on a predefined receive path selection criteria, aswell as means for establishing a connection, such as, but not limitedto, an electrical connection, between the selected bus and the non-1553receiver block 50. Predefined receive path selection criteria ofselecting a non-1553 receive path are defined herein as any designcriteria aimed at indicating the appropriate receive path, from aplurality of data buses to a non-1553 receiver.

FIG. 3 illustrates the flowchart of a method of receiving non-1553signals within the 1553 communications system 10, according to anembodiment of the invention. According to this embodiment, the methodcomprises the step of monitoring the performance of the primary bus 20and of the redundant bus 30, as shown at 61. Preferably, the monitoringstep is performed periodically, based on metrics that may include,without limitation, Signal to Noise Ratio (SNR), Bit Error Rate (BER),channel capacity etc. Based on the values obtained during the monitoringstep, preferably averaged over appropriate time intervals, a selectionof an appropriate receive path, from the primary bus to the receiver orfrom the redundant path to the receiver, as shown at 62, is made.Finally, once a receive path is selected, the connection between thecorresponding bus and the non-1553 receiver is established, step 63,allowing for non-1553 signals to be received at the non-1553 receiver50.

According to a preferred embodiment, the higher performance bus will beselected as the bus from which to receive signals. For example, underno-bus fault conditions, 1553 signals might be transmitted on theprimary bus, leaving the redundant bus available for unfetteredtransmission of non-1553 signals. When the same bus must be used forboth 1553 and non-1553 signals, a multiplexing scheme such as TimeDivision Multiplexing might be used, although this may not be necessary.

FIG. 4 illustrates a 1553b communications system 12 according to apreferred embodiment of the invention. The 1553b communication system 12is built and operates in accordance to the 1553b standard. The 1553bcommunication system 12 comprises a primary bus (Bus A) 21 and aredundant bus (Bus B) 31, a 1553b Bus Controller (BC) 101 and aplurality of 1553b Remote Terminals (RT) 115, 117 exchanging 1553bsignals along buses 21, 31. In addition, the 1553b system 12 comprisesan OFDM Bus Controller 102 and a plurality of OFDM Remote Terminals 114,116.

Each 1553b terminal comprises a 1553b Transmitter 70, connecting via aswitch to either the primary bus 21 or the redundant bus 31, and acouple of 1553b receivers 81, 82. Each OFDM terminal comprises an OFDMTransmitter 42, connected to the primary bus 21 and to the redundant bus31, and an OFDM receiver 52 that can connect via a switch to either bus.

FIG. 5 shows a detailed block diagram of a 1553b terminal in the 1553bsystem 12. The 1553b transmitter 70 comprises a controller block, anencoder, and an analog front end (AFE) block, containing all thecircuitry for filtering, for converting the signal from digital toanalog and for coupling the signal to the primary bus (Bus A) or theredundant bus (Bus B) via a switch. Each 1553b receiver 81, 82 comprisesan AFE block performing necessary filtering and conversion from analogto digital, a decoder block, and a controller block.

FIG. 6 illustrates an OFDM terminal according to a preferred embodimentof the invention. The OFDM Transmitter 42 includes a forward errorcorrection (FEC) unit A for adding FEC bits to an input data bit stream.Forward Error Correction (FEC) may consist of Reed-Solomon,convolutional or other types of coding schemes that will be recognizedby someone skilled in the art. The FEC unit A is followed by a mappingblock B which maps the encoded bits to frequency domain sub-carriers,which are then transformed to a time domain digital signal (symbol) byan inverse Fast Fourier Transform (IFFT) unit C, which will berecognized by those skilled in the art as means for an efficientimplementation of the inverse discrete Fourier Transform (DFT)algorithm. Preferably, the number of bits that are allocated toparticular tones is chosen to match the signal to noise conditions ofthe channel.

The symbols are then received by a preamble unit D, which pre-pends tothem a preamble, consisting of a number of synchronization symbols. Thepreamble allows for synchronization of the transmitted waveform at thereceiver, as well as to enable analog gain control (AGC) and channelresponse estimation. Furthermore, a cyclic prefix is also usually addedto the OFDM symbols. Next, the symbols are appropriately shaped by asymbol shaper E before conversion to an analog signal by the analogfront end (AFE) F. The symbol shaping may include operations such aswidowing and filtering. Following, the OFDM symbols represented asdigital signals are converted to analog signals by the analog front end(AFE) F, comprising a digital to analog converter and appropriate analogfilters. The AFE may further include an IF/RF mixing stage to convertthe signal to higher frequencies.

The OFDM Receiver 52 selects the analog signal from the primary bus 21or redundant bus 31, as discussed above. Then, the appropriate RF/IFstages are used to convert the signal to a baseband signal which is thenfiltered and converted from the analog domain to a digital signal by ananalog front end (AFE) which includes an analog to digital converter P.An Automatic Gain Control block (AGC) O controls the input signal levelbased on power metrics estimated from the synchronization symbols. AFast Fourier Transform (FFT) is applied to the sampled signal by an FFTblock N, preferably with the timing of the FFT based on the detectionand timing estimation of the synchronization symbols performed by aDetection Synchronization block S. Channel estimation is achieved basedon the synchronization symbols and is used by a De-Modulator M to removephase and amplitude distortion effects of the channel. Channelequalization is next performed in the frequency domain. A De-Mappingfunction L converts the demodulated frequency domain sub-carriers tocoded data bits, followed by the corresponding forward error correctionblock R to correct any bit errors (if correctable). The decoded databits are passed to higher communications layers.

According to the preferred embodiment of the invention, OFDM modulationis used to better utilize the available bandwidth on the bus, creatingan “overlay” network to operate concurrently and without disturbingexisting 1553b communications. This is accomplished by utilizing OFDMsignals with little energy (low PSD) in a 1553b high-energy frequencyband and with a relatively constant Power Spectral Density (PSD) in1553b low-energy frequency band. FIG. 7 is a theoretical representationof the PSD of a transmitted OFDM signal relative to a 1553b transmittedwaveform. As illustrated, the OFDM waveforms are configured to utilizethe frequency band from 5 to 35 MHz where 1553b side lobes of a given1553b system are relatively low. In addition, the OFDM signals havelittle energy in the 0 to 5 MHz band. Therefore, interference betweenOFDM communications and existing 1553b communications is minimized.Alternate embodiments contemplate configuration of OFDM signals withdifferent frequency bands, including an OFDM waveform configured toutilized the frequency band from about 5 MHz to a frequency greater than35 MHz, such as 40 MHz.

FIG. 8 illustrates representative PSD's at a receiver of both a 1553bsignal and OFDM signal for a particular bus configuration. In thisexample, the Signal to Noise Ratio (SNR) has an acceptable level in thefrequency band below 5 MHz for a 1553b receiver to decode the 1553bsignal. As well, the SNR has an acceptable level in the frequency bandabove 5 MHz for an OFDM receiver to decode the OFDM signal. It will beunderstood by those skilled in the art of data communications that thefrequency and bandwidth of the OFDM communications devices can be chosento match the channel conditions of a given 1553b bus to ensure reliablecommunications for both 1553b and OFDM systems.

When both 1553b and OFDM signals are transmitted on the same bus,relative powers at a receiver would depend on the network topology andthe particular locations of transmitters and receivers. A network ofthis topology and components is generally frequency selective in nature.A transceiver is generally transformer coupled to the bus stub (cableconnection to the main bus) and the connecting stubs can be eithertransformer coupled or direct coupled using isolation resistors only tothe main bus.

Referring back to FIG. 4, bus fault design is herein defined aspredefined operation of the communication system in the event of busfaults. Examples of bus faults include, without limitation, a brokenwire or connector or an issue with a terminal itself. A dual redundantscheme of 1553b communication over system 12 is as follows: 1553bdevices transmit on Bus A under no bus fault conditions and receive fromboth Bus A and Bus B. Each OFDM device transmits the same signal on bothBus A and Bus B and receives on Bus B under no bus fault conditions.When bus faults occur on Bus A 1553b devices will switch to Bus B fortransmission, under BC control. In most 1553b applications, a bus faultis determined on a terminal by terminal basis; however, other bus faultdetection designs are not excluded. When the 1553b BC 101 detects thatone of the 1553b RT's does not respond on the primary bus 21, itre-sends the command to that RT to transmit on the redundant bus 31.Occasionally, the 1553b BC may also send a command on the redundant bus31 to test the integrity of the wire.

In order to select a receive path, the OFDM receiver 52 of the OFDMdevice 114, while connected to the secondary (redundant) bus 31,periodically monitors the secondary bus for performance via non-1553receive path selection unit 65. The monitoring is performed based on apredefined design scheme or predefined selection criteria, specifyingacceptable performance level for selected metrics. The metrics used forthis determination can include but are not limited to SNR, Bit ErrorRate and capacity. The metrics could be monitored and averaged over anappropriate time interval. Detection of performance of the redundant busbelow acceptable levels, triggers switching the connection of OFDMreceiver 52 from the secondary bus 31 to the primary bus 21, thusestablishing an alternate receive path. Switching to the other bus couldalso be initiated by failing to decode a message on the currentlyconnected bus. Alternately, both buses could be monitored at the sametime, and a receive path between the better performing bus and thereceiver could be established accordingly, as described earlier inreference to FIG. 3 (see step 61).

In summary, embodiments of the present invention allow for an overlay ofa non-1553 communication scheme over legacy 1553 systems, with minimalimpact to the 1553 communications, thereby providing the ability ofenhancing the throughput of existent 1553 systems and of adding newdigital equipment, without rewiring.

Furthermore, a dual-redundant scheme employing a single non-1553transmitter and single non-1553 receiver per non-1553 transceiver ispresented. Therefore, additional benefits compared to 1553b dualredundancy architecture include lower power, smaller size, less heatdissipation requirements and lower design complexity. It will be obviousto those skilled in the art of data communications that the dualredundant architecture in FIG. 4 may scale to more than 2 buses.

Although the present invention has been described in considerable detailwith reference to certain preferred embodiments thereof, other versionsare possible. Therefore, the spirit and scope of the appended claimsshould not be limited to the description of the preferred embodimentscontained herein.

1. Within a 1553 data communication system having a primary data bus anda redundant data bus, an OFDM data communication overlay systemcomprising: an OFDM bus controller terminal and an OFDM remote terminal,wherein each OFDM terminal includes: an OFDM transmitter block connectedto the primary bus and the redundant bus for sending OFDM signals; anOFDM receiver block for receiving OFDM signals; and an OFDM receive pathselection block for selectively establishing a receive path between theprimary data bus or the redundant data bus and the OFDM receiver blockaccording to predefined receive path selection criteria, wherein theOFDM signals are Power Spectral Density (PSD) configurable according tothe topology of the 1553 data communication system and are configured tohave a low PSD in a 1553b high energy frequency band and a substantiallyflat high PSD in a 1553b low energy frequency band.
 2. The OFDMdatacommunication overlay system of claim 1, wherein the OFDM datacommunication system comprises a plurality of OFDM remote terminalscommunicating with the OFDM bus control terminal over one of the primarydata bus and the redundant data bus.
 3. The OFDM data communicationoverlay system of claim 1, wherein the 1553 data communication isaccording to MIL-STD-1553B communication standard.
 4. The OFDM datacommunication overlay system of claim 1, wherein the 1553 datacommunication is according to Notice 2 of MIL-STD-1553B communicationstandard.
 5. The OFDM data communication overlay system of claim 1,wherein said OFDM signals are bandwidth configurable according tochannel conditions of the 1553 data communication system.
 6. The OFDMdata communication overlay system of claim 1, wherein said 1553b highenergy band is from approximately 0 MHz to approximately 5 MHz.
 7. TheOFDM data communication overlay system of claim 1, wherein the OFDMsignals have a substantially high flat PSD from approximately 5 MHz to afrequency approximately equal to or greater than 35 MHz.
 8. The OFDMdata communication overlay system of claim 1, wherein said receive pathselection criteria include performance metrics of said OFDM signals onsaid buses.
 9. The OFDM data communication overlay system of claim 8,wherein said performance metrics include one or more of Bit Error Rate(BER), Signal to Noise ratio (SNR), channel capacity metrics.
 10. TheOFDM data communication overlay system of claim 9, wherein the OFDMreceive path selection unit monitors performance metrics of said OFDMsignals periodically.
 11. The OFDM data communication overlay system ofclaim 9, wherein the OFDM receive path selection unit further averagesmonitored performance metrics of said OFDM signals over predefined timeintervals.
 12. A 1553 data communication system comprising: a primarydata bus; a redundant data bus; A 1553 bus controller terminal and aplurality of 1553 remote terminal, each 1553 terminal comprising: A 1553Transmitter block; an analog switch, for selectively connecting the 1553transmitter block either to the primary bus or to the redundant busaccording to a predefined receive path selection criteria and accordingto bus fault design; a first 1553 receiver block for receiving 1553signals from the primary bus, under no-bus fault conditions; and Asecond 1553 receiver block for receiving signals from the redundant busunder bus-fault conditions; an OFDM bus controller terminal and aplurality of OFDM remote terminals, each OFDM terminal comprising: AnOFDM transmitter block connected to the primary bus and the redundantbus for sending OFDM signals on the primary bus and on the redundantbus; An OFDM receiver block; and an OFDM receive path selection blockfor monitoring the performance of the primary bus and of the redundantbus and for establishing a receive path between the OFDM receiver blockand either the primary bus or the redundant bus based on performancemetrics.
 13. The 1553 data communication system as in claim 12, whereinthe OFDM signals are bandwidth configurable and PSD configurable OFDMsignals, wherein the bandwidth and PSD of OFDM signals are configuredaccording to channel conditions of the primary bus and of the redundantbus.
 14. The 1553 data communication system as in claim 12, wherein theperformance monitoring comprises periodically determining metric values,wherein metrics are selected from the group of SNR, BER, capacity andaveraging said metric values over a predetermined time interval.